EP2922986B1 - Method for the nanostructuring and anodization of a metal surface - Google Patents

Description

Field of the invention

The invention relates to a method for nanostructuring and oxidation of a surface comprising an anodizable metal and / or anodizable metal alloy, both of which may be coated with an oxide layer, by means of laser or particle radiation in an inert or reactive atmosphere and subsequent anodization.

Background of the invention

The anodization of metals and metal alloys is a well-known method. In this, a material of an anodizable metal or anodizable metal alloy is used as an anode in an electrolytic cell, which further comprises a cathode connected to the anode (usually made of precious metal) and an electrolyte with a suitable oxidizing agent. Upon application of a voltage, the surface of the metal or metal alloy is oxidized. In electrolytes which also contain a metal oxide redissolving additive in a suitable concentration, under suitable conditions, the process may be conducted so that a smaller portion of the oxidized surface is continually redissolved by the electrolyte, while a larger portion of the surface is still oxidized , In this way, structures of micrometer or nanometer dimensions, in the special case of titanium in the form of nanotubes, can be created on the oxidized surface.

In many cases, however, these surfaces comprise areas that do not have nanostructures after anodization.

Out DAOAI WANG ET AL: "Engineering a Titanium Surface with Controllable Oleaphobicity and Switchable Oil Adhesion", JOURNAL OF PHYSICAL CHEMISTRY C, Vol. 114, No. 21, 3 June 2010 (2010-06-03), pages 9938-9944, XP055123253 , ISSN: 1932-7447, DOI: 10.1021 / jp1023185 discloses a method for producing oleophobic nanostructures on titanium surfaces, in which first the surface is microstructured with a laser beam having a wavelength of 1064 nm and a repetition rate of the radiation pulses of 10 kHz and a pulse length of the pulses of 5-25 ns to form a pattern at different depths, with the microstructured surface subsequently anodized.

Out MACAK JM ET AL: "Influence of different fluoride containing electrolytes on the formation of self-organized titania nanotubes by TI anodization", JOURNAL OF ELECTROCERAMICS; KLUWER ACADEMIC PUBLISHERS; BO, Vol 16, No. 1, 1 February 2006 (2006-02-01), pages 29-34 XP019208330, ISSN: 1573-8663; DOI: 10.1007 / S10832-006-3904-0 , the formation of nanotubes on Ti surfaces is known by anodization without previous structuring.

From the US 2008/011175 A1 For example, a method for producing a microstructure on an aluminum surface is known in which the surface is pre-structured by sand blasting or by means of a laser and then anodized.

From the US 2001/0010973 A1 For example, there is described a method for producing regularly arranged narrow very linear pores, in which first the surface is irradiated with a particle beam in the form of an electron beam or ion beam such that discrete starting points for forming the pores are spaced apart by a distance of 5 nm to 1000 nm Jobs are trained. Subsequently, anodic oxidation is performed on the thus irradiated workpiece to form the narrow pores in the workpiece.

Summary of the invention

The invention relates to a method according to claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

• wenn mit einem Laserstrahl abgetastet wird und die Impulslänge der Laserimpulse t etwa 0,1 ns bis etwa 2000 ns ist,
  • ein ε-Wert von etwa 0,07 ≤ ε ≤ etwa 2300,
  wobei $$\epsilon =\frac{P_P^2\cdot \sqrt{P_m}\cdot f\cdot \alpha \cdot \sqrt{t}\cdot \sqrt{\kappa }}{d^2\cdot \sqrt{v}\cdot \sqrt{T_V}\cdot \sqrt{c_P}\cdot \sqrt{\lambda }}\cdot {10}^3$$
  
  oder, wenn mit einem Laserstrahl bei einer Wellenlänge des Lasers λ von etwa 100 ≤ λ ≤ etwa 11000 nm abgetastet wird und die Impulslänge der Laserimpulse t < etwa 0,1 ns, ein _ε1-Wert von etwa 0,5 ≤ ε₁ ≤ etwa 1650,
  wobei $${\epsilon }_1=\frac{P_P\cdot \sqrt{P_m}\cdot f\cdot \alpha \cdot \sqrt{t}\cdot \sqrt{\kappa }}{d^2\cdot \sqrt{v}\cdot \sqrt{T_v}\cdot \sqrt{c_P}}\cdot {10}^3$$
  
  worin in Gleichung 1 und Gleichung 2:
  • P_p: Impulsspitzenleistung der austretenden Strahlung [kW];
  • t: Impulslänge der Impulse [ns];
  • f: Repetitionsrate der Strahlungsimpulse [kHz];
  • v: Abtastgeschwindigkeit an der Werkstückoberfläche [mm/s];
  • d: Durchmesser der energetischen Strahlung an der Materialoberfläche [µm];
  • α: Absorption der energetischen Strahlung des bestrahlten Materials [%] bei der eingestrahlten Wellenlänge bei Normalbedingungen;
  oder,
  wenn mit einem Teilchenstrahl abgetastet wird, eine ε₂-Wert von etwa 0,5 ≤ ε₂ ≤ etwa 1550,
  wobei $${\epsilon }_2=\frac{P_m^2\cdot \sqrt{\kappa }\cdot \alpha }{\sqrt{d^3}\cdot \sqrt{v}\cdot \sqrt{T_v}\cdot \sqrt{c_P}}\cdot {10}^2$$
  
  worin in Gleichung 3:
  • v: Abtastgeschwindigkeit an der Werkstückoberfläche [mm/s];
  • d: Durchmesser der energetischen Strahlung an der Materialoberfläche [µm]; mit der Maßgabe, dass d/v < etwa 7000 ns;
  • α: Absorption der energetischen Strahlung des bestrahlten Materials [%] bei Normalbedingungen;
  und in Gleichung 1, Gleichung 2 und Gleichung 3:

• P_m: Mittlere Leistung der austretenden Strahlung [W];
• T_v: Verdampfungs- bzw. Zersetzungstemperatur des Materials [K] bei Normaldruck
• c_p: Spezifische Wärmekapazität [J/kgK] bei Normalbedingungen
• κ: Spezifische Wärmeleitfähigkeit [W/mK] bei Normalbedingungen und gemittelt über die verschiedenen Raumrichtungen,

wobei die Atmosphäre, in der das Verfahren stattfindet,
Vakuum oder ein gegenüber der Oberfläche unter den Verfahrensbedingungen inertes Gas oder Gasgemisch ist oder
ein gegenüber dem Metall und/oder der Metalllegierung und/oder der Oxidschicht auf dem Metall oder/oder der Metalllegierung der Oberfläche unter den Verfahrensbedingungen reaktives Gas oder Gasgemisch ist, durch welches das Metall und/oder die Metalllegierung und/oder die Oxidschicht auf dem Metall oder/oder der Metalllegierung bei oder nach dem Abtasten mit dem Laser- oder Teilchenstrahl gegenüber seiner bzw. ihrer Zusammensetzung vor dem Abtasten mit dem Laser- oder Teilchenstrahl chemisch modifiziert wird;
und die Oberfläche anschließend durch Eintauchen in eine Elektrolytlösung, die sowohl ein Oxidationsmittel als auch ein das Oxid wieder auflösendes Agens enthält, das gegebenenfalls identisch mit den Oxidationsmittel sein kann, Verbinden mit einer Kathode und Anlegen einer Spannung anodisiert wird.The invention describes a method for nanostructuring and oxidation of a surface of a material comprising an anodizable metal and / or anodizable metal alloy, both of which may be at least partially coated with an oxide layer, wherein the surface of the metal and / or the metal alloy and or the oxide layer on the metal or / and the metal alloy which is accessible for laser irradiation or for irradiation with a particle beam and on which the structures are to be produced, with a pulsed laser beam or a continuous particle beam consisting of an electron beam or Ion beam or a beam of uncharged particles or a combination thereof is scanned completely one or more times in such a way that adjacent light spots of the laser beam or scanning spots of the particle beam abut each other or overlap gap, the following conditions be respected:

• when sampled with a laser beam and the pulse length of the laser pulses t is about 0.1 ns to about 2000 ns,
  • an ε value of about 0.07 ≤ ε ≤ about 2300,
  in which $$\epsilon =\frac{P_P^2\cdot \sqrt{P_m}\cdot f\cdot \alpha \cdot \sqrt{t}\cdot \sqrt{\kappa }}{d^2\cdot \sqrt{v}\cdot \sqrt{T_V}\cdot \sqrt{c_P}\cdot \sqrt{\lambda }}\cdot {10}^3$$
  
  or, when scanning with a laser beam at a wavelength of the laser λ of about 100 ≦ λ ≦ about 11000 nm and the pulse length of the laser pulses t <about 0.1 ns, an _ε1 value of about 0.5 _≦ ε ₁ ≦ about 1650,
  in which $${\epsilon }_1=\frac{P_P\cdot \sqrt{P_m}\cdot f\cdot \alpha \cdot \sqrt{t}\cdot \sqrt{\kappa }}{d^2\cdot \sqrt{v}\cdot \sqrt{T_v}\cdot \sqrt{c_P}}\cdot {10}^3$$
  
  wherein in Equation 1 and Equation 2:
  • P _p : peak pulse power of the emitted radiation [kW];
  • t: pulse length of the pulses [ns];
  • f: repetition rate of the radiation pulses [kHz];
  • v: scanning speed on the workpiece surface [mm / s];
  • d: diameter of the energetic radiation at the material surface [μm];
  • α: absorption of the energetic radiation of the irradiated material [%] at the irradiated wavelength under normal conditions;
  or,
  when it is scanned with a particle beam, an ε ₂ value of approximately 0.5 ≤ ε ≤ ₂ about 1550,
  in which $${\epsilon }_2=\frac{P_m^2\cdot \sqrt{\kappa }\cdot \alpha }{\sqrt{d^3}\cdot \sqrt{v}\cdot \sqrt{T_v}\cdot \sqrt{c_P}}\cdot {10}^2$$
  
  wherein in equation 3:
  • v: scanning speed on the workpiece surface [mm / s];
  • d: diameter of the energetic radiation at the material surface [μm]; with the proviso that d / v <about 7000 ns;
  • α: absorption of the energetic radiation of the irradiated material [%] under normal conditions;
  and in equation 1, equation 2 and equation 3:

• P _m : mean power of the exiting radiation [W];
• T _v : Evaporation or decomposition temperature of the material [K] at normal pressure
• c _p : Specific heat capacity [J / kgK] under normal conditions
• κ: specific thermal conductivity [W / mK] under normal conditions and averaged over the different spatial directions,

the atmosphere in which the process takes place
Vacuum or a gas or gas mixture inert to the surface under the process conditions, or
a gas or gas mixture reactive with the metal and / or the metal alloy and / or the oxide layer on the metal and / or the metal alloy of the surface under the process conditions, through which the metal and / or the metal alloy and / or the oxide layer on the metal and / or the metal alloy is chemically modified during or after scanning with the laser or particle beam relative to its or their composition prior to scanning with the laser or particle beam;
and then the surface is anodized by immersion in an electrolyte solution containing both an oxidizing agent and an oxide redissolving agent, which may optionally be identical to the oxidizing agent, bonding to a cathode and applying a voltage.

Brief description of the figures

• FIG. 1 shows the surface of a Ti-6AI-4V alloy after simple anodization.
• FIG. 2 shows the surface of a Ti-6Al-4V alloy after nanostructuring by laser beam.
• FIG. 3 shows the surface of a Ti-6AI-4V alloy after nanostructuring by laser beam in argon atmosphere and subsequent anodization.
• FIG. 4 shows the surface of a Ti-6AI-4V alloy after nanostructuring by laser beam under oxygen atmosphere.
• FIG. 5 shows the surface of a Ti-6AI-4V alloy after nanostructuring by laser beam under oxygen atmosphere and subsequent anodization.

Detailed description

It has surprisingly been found that sequential treatment of a metal or metal alloy surface optionally having an oxide coating of a material can be provided by nanostructuring by laser or particle radiation in an inert or reactive atmosphere followed by anodization on the entire surface nanostructures of an oxide of the metal or metal alloy which in the case of titanium may be in the form of nanotubes. After this treatment, no areas of the surface remain that have no nanostructuring. Furthermore, it has been found that the nanostructures thus produced are finer and the nanostructure more homogeneous than those produced solely by anodization of the material.

The roughening or structuring in the nanometer range of surfaces is particularly important for a good adhesion of adhesives, paints, biological tissue and other coatings, such as heat protection layers and metallic adhesion promoter layers, essential.

A single or multiple irradiation with a pulsed laser beam or a continuous particle beam in an inert or reactive atmosphere under the conditions mentioned in the method described above can produce nanostructured surfaces suitable for good adhesion e.g. adhesives, lacquers, solder, sealants, bone cement, adhesion promoters or biological tissue as well as other coatings such as coatings to protect against chemical or thermal exposure. If necessary, even by sole joining under pressure, two materials can be adhesively bonded together if such nanostructures have been produced on at least one material.

The surface-structured surfaces produced by laser or particle radiation which are chemically modified when working in a reactive atmosphere relative to the starting surface may vary Embodiment generally open-pored, fissured and / or fractal-like nanostructures, such as open-pore hill and valley structures, open-pore undercut structures and cauliflower or bulbous structures have. These structures typically cover the entire radiation treated metal or metal alloy surface.

The scanning of the output surface with the laser or particle beam can be repeated one or more times with the same process parameters and the same laser or particle beam or with different process parameters with the same laser or particle beam or with different laser and / or particle beams with the same process parameters or with different process parameters be performed. By repeated sampling under certain circumstances an even finer structure can be produced.

It must be mentioned that naturally only those surface areas can be treated that can be achieved by a laser or particle beam. Regions that are completely "in the shade" (e.g., undercut geometries) can not be patterned in the manner described herein.

Often, the starting surface comprising the metal or metal alloy and / or optionally an oxide layer thereon is not pretreated or cleaned prior to scanning with the laser or particle beam, but may also be e.g. be cleaned or pickled with a solvent.

Structuring with a laser or particle beam alone, as noted above, provides many materials, especially for good adhesion. However, there are also many instances where, along with nanostructuring, a simultaneous oxidation of the surface is desired or required, which is more uniform and / or has a greater layer thickness and in particular is even more porous than one optionally after treatment with the laser or Particle jet remaining oxide layer (if it has been assumed by an oxide-coated surface).

The metal and / or metal alloy encompassed by the surface, which may optionally be at least partially coated with an oxide layer, are selected from anodisable metals and / or metal alloys. These include in particular aluminum, titanium, magnesium, iron, cobalt, zinc, niobium, zirconium, hafnium, tantalum, vanadium and / or their alloys and steel. In addition to pure titanium, in particular cobalt-chromium alloys, cobalt-chromium-molybdenum alloys and the alloys Ti-6Al-4V, Mg-4Al1-Zn, Ta-10W, Al 2024 (Al-4.4Cu-1.5Mg-0.6 Mn) and V2A steel (X5CrNi18-10).

The metal and / or the metal alloy, which may optionally be at least partially coated with an oxide layer, may also be present in a metal-ceramic composite or a composite of a metal and / or a metal alloy containing the heat-conductive carbonaceous and / or boron nitride-containing Contain particles and / or fibers present.

The present in the process according to the invention pressure is generally in the range of about 10 ^-17 bar to about 10 ^-4 bar when working in vacuo, and in the range of about 10 ^-6 bar to about atmospheric pressure at particle beams and up to about 15 bar at Laser beams when operating in an atmosphere of intentionally added inert or reactive gas or gas mixture. The temperature outside the laser or particle beam is generally in the range of about -50 ° C - about 350 ° C (in the jet of course much higher temperatures may be present).

The evaporation or decomposition point at atmospheric pressure, the specific heat capacity c _p under normal conditions, the averaged over the different spatial directions specific thermal conductivity κ under normal conditions and the laser radiation at the wavelength of the laser radiation dependent absorption of the energy radiation of the irradiated material α under normal conditions, the in the above-mentioned expression for ε or ε ₁ or ε ₂ are used, are material properties of the treated metal or the treated metal alloy. In the case of metals or metal alloys covered with an oxide layer, the data of the underlying metal or metal alloy are used for the evaporation or decomposition point at normal pressure, the specific heat capacity c _p under normal conditions and the specific thermal conductivity κ under normal conditions.

Equation 1

Values of ε, which must result from the parameters of Equation 1 given above, in order to produce the desired surface structuring according to the invention, are preferably about 0.07 ≦ ε ≦ about 2000, more preferably about 0.07 ≦ ε ≦ about 1500 ,

Hereinafter, preferred parameters of the method of the invention are given for equation 1. It must be emphasized that all parameters can be varied independently.

The laser wavelength λ may be about 100 nm to about 11000 nm.

The pulse length of the laser pulses t is preferably about 0.1 ns to about 300 ns, more preferably about 5 ns to about 200 ns.

The pulse peak power of the exiting laser radiation Pp is preferably about 1 kW to about 1800 kW, more preferably about 3 kW to about 650 kW.

The average power of the exiting laser radiation P _m is preferably about 5 W to about 28,000 W, more preferably about 20 W to about 9500 W.

The repetition rate of the laser pulses f is preferably about 10 kHz to about 3000 kHz, more preferably about 10 kHz to about 950 kHz.

The scanning speed at the workpiece surface v is preferably about 30 mm / s to about 19000 mm / s, more preferably about 200 mm / s to about 9000 mm / s.

The diameter of the laser beam on the workpiece d is preferably about 20 μm to about 4500 μm, more preferably about 50 μm to about 3500 μm.

Equation 2

The values of ε ₁ , which must result from the parameters of Equation 2 given above, so that the desired surface structuring according to the invention is produced, are preferably approximately 0.07 ≦ ε ₁ ≦ approximately 1500, more preferably approximately 0.9 ≦ ε ₁ ≤ about 1200.

The laser wavelength λ is about 100 nm to about 11000 nm.

Hereinafter, preferred parameters of the method of the invention are given for equation 2. It must be emphasized that all parameters can be varied independently.

The pulse length of the radiation t is preferably about 0.005 ns to about 0.01 ns, more preferably about 0.008 ns to about 0.01 ns.

The peak pulse power of the exiting radiation Pp is preferably about 100 kW to about 30,000 kW, more preferably about 150 kW to about 25,000 kW.

The average power of the exiting radiation P _m is preferably about 5 W to about 25,000 W, more preferably about 20 W to about 9500 W.

The repetition rate of the radiation f is preferably about 100 kHz to about 80,000 kHz, more preferably about 120 kHz to about 20,000 kHz.

The scanning speed at the workpiece surface v is preferably about 30 mm / s to about 60,000 mm / s, more preferably about 200 mm / s to about 50,000 mm / s.

The diameter of the laser beam on the workpiece d is preferably about 20 μm to about 4500 μm, more preferably about 50 μm to about 3500 μm.

Pulsed solid-state lasers such as Nd: YAG (λ = 1064 nm or 533 nm or 266 nm), Nd: YVO ₄ (λ = 1064 nm), diode lasers with eg λ = 808 nm, gas lasers, such as eg excimer lasers, with, for example, KrF (λ = 248 nm) or H ₂ (λ = 123 nm or 116 nm) or a CO ₂ laser (10600 nm).

Equation 3

The values of ε ₂ which must result from the parameters of Equation 3 given above in order to produce the surface structuring according to the invention are preferably about 0.07 ≦ ε ₂ ≦ about 1400, more preferably about 0.9 ≦ ε ₂ ≤ about 1100.

Hereinafter, preferred parameters of the method of the invention are given for equation 2. It must be emphasized that all parameters can be varied independently.

The average power of the exiting radiation P _m is preferably about 1 W to about 25,000 W, more preferably about 20 W to about 9500 W.

The scanning speed at the workpiece surface v is preferably about 100 mm / sec to about 8,000,000 mm / sec, more preferably about 200 mm / sec to about 7,000,000 mm / sec.

The diameter of the particle beam on the workpiece d is preferably about 20 μm to about 4500 μm, more preferably about 50 μm to about 3500 μm.

The ratio of beam diameter to scan speed is limited, namely, d / v <about 7000 ns.

Suitable radiation sources for electron and ion beams and beams of uncharged particles are known to those skilled in the art.

The atmosphere in which the process according to the invention is used may be a vacuum or a gas or gas mixture which is inert to the surface under the process conditions, the inert gases being a noble gas, eg argon, helium or neon, depending on the surface and process conditions, or in many cases also nitrogen or CO ₂ , or a mixture of these gases. The inert gas or gas mixture is selected so that it does not react with the metal, metal alloy or oxide layer on a given metal, metal alloy or oxide layer thereon under the pressure and temperature operating conditions.

The pressure is when working in a vacuum without addition of gas, preferably at 10 ^-17 to 10 ^-4 bar. When working with inert gas additive, the pressure is generally 10 ^-6 to 1 bar when using particle beams and up to 15 bar when using laser beams. Ambient pressure and temperature are preferred if permitted by the given surface.

On the other hand, the atmosphere in which the process according to the invention is carried out may comprise a reactive gas which chemically modifies the surface material according to the invention. The reactive gases in which the process can be carried out include, for example, inorganic gases or gas mixtures such as hydrogen, air, oxygen, nitrogen, halogens, carbon monoxide, carbon dioxide, ammonia, nitrogen monoxide, nitrogen dioxide, nitrous oxide, sulfur dioxide, hydrogen sulfide, boranes and / or silanes (eg monosilane and / or disilane).

Organic gases or gases with organic groups can also be used. These include e.g. lower, optionally halogenated alkanes, alkenes and alkynes, such as methane, ethane, ethene (ethylene), propene (propylene), ethyne (acetylene), methyl fluoride, methyl chloride and methyl bromide, and also methylamine and methylsilane. Also, a mixture of an inorganic and organic or organic group-containing gas may be used.

When a gas mixture is present, it is sufficient that a gas component thereof or a mixture of a plurality of gas components is a reactive gas; the remainder may be an inert gas, usually a noble gas. The concentration of the reacting gas or gas mixture may be of a few ppb, e.g. 5 ppb, up to more than 99 vol% vary.

The selection of the reactive gas or gas mixture, of course, depends on the intended modification of the surface material of the invention. If an oxide-containing surface is to be reduced, e.g. Of course, to introduce hydroxide groups, one will use a reducing gas such as hydrogen as the reactive gas (optionally in admixture with an inert gas). For oxidation of the surface, however, e.g. consider an oxygen-containing gas. The person skilled in the art knows which reactive gas to choose in order to achieve a desired effect on a given surface material according to the invention.

The pressure of the reactive gas or gas mixture, optionally including only a reactive gas portion, is generally in the range of about 10 ^-6 bar to about 1 bar when using a particle beam and up to about 15 bar when using a laser beam. Atmospheric pressure is preferred. It may be used at gas temperatures that are generally outside the laser beam in the range of about -50 ° C to about 350 ° C. Of course, much higher temperatures can occur in the laser beam.

Whether a chemical modification of a given surface material has been carried out, the skilled person can by suitable analysis methods, such as X-Ray Photoelectron Spectroscopy (XPS), EDX (energy dispersive X-ray analysis), FTIR spectroscopy, Time of Flight Secondary Ion Mass Spectrometry (TOF -SIMS), EELS (electron energy loss spectroscopy), HAADF (high angle annular dark field) or NIR (near infrared spectroscopy) in experience.

When the metal and / or the metal alloy on the material surface has been nanostructured as described above, it is subjected to anodization in which the workpiece forming the anode is immersed in an electrolytic solution, connected to a cathode usually comprising noble metal, and then put on a Tension anodized.

In general, the generation of highly porous and / or present in the form of nanotubes oxide layers by means of anodization that the electrolyte must have a dual function: on the one hand continuously oxidize the metal or metal alloy and on the other hand partially dissolve the oxide formed again. This results in highly porous or nanotube structures. Accordingly, the electrolyte must contain an effective oxidizing agent and at the same time an agent which provides for the redissolution of the oxide.

The person skilled in the art knows numerous electrolytes and process conditions for the anodization.

In the anodization, an electrolytic solution containing, as the oxidizing agent, usually either an oxidizing inorganic or organic acid or an oxidizing acid salt or a hydroxide-based alkaline oxidizing agent is used. The usable inorganic acids and acidic salts include, for example, sulfuric acid, chromic acid, phosphoric acid, nitric acid and ammonium sulfate, to the usable organic acids such as toluenesulfonic acid, benzenesulfonic acid and tartaric acid. Hydrochloric acid can be used to set a suitable pH. Hydroxide-containing alkaline oxidizing agents are often based on caustic soda.

To achieve a micro or nanostructure, a portion of the oxide formed is redissolved. This can be done with an acid, which may be another acid or, in some cases, the same acid as that used for oxidation, or with an acidic salt. Often, the counterion of the acid or the anion of the salt is a complexing agent for the anodized metal or anodized metal alloy.

Thus, tartaric acid, the anion of which is a complexing agent, can be used as the oxide dissolving agent, for example, in conjunction with phosphoric acid as the (further) oxidizing agent. Frequently, hydrofluoric acid or, if appropriate, ammonium fluoride is also used to re-dissolve the oxide.

An example in which the oxidizing acid is identical to the oxide redissolving agent is phosphoric acid in the case of anodization of aluminum, the sole use of which results in the formation of a micro or nanostructure.

The concentrations of the oxidizing agent and the oxide-dissolving agent, which is often used in a lower molar concentration compared to the oxidizing agent, and the pH of the electrolytic solution vary depending on the metal or metal alloy and the desired layer thickness and porosity. This also applies to the voltage and temperature used in the respective process.

For some metals, in particular titanium and titanium alloys, ammonium sulfate can be advantageously used as the oxidizing agent together with ammonium fluoride as the oxide-dissolving agent, which avoids the handling of the extremely toxic hydrofluoric acid and is particularly preferred in the process according to the invention.

For example, in this preferred process variant, the aqueous electrolyte generally comprises 10 to 1000 g / l, eg 100 to 500 or 160 g / l, preferably 120 to 140 g / l and especially 130 g / l of ammonium sulfate and generally 0.1 to 10 g / l, preferably 2 to 6 g / l and in particular Ammonium fluoride, wherein the temperatures are generally at 20 to 50 ° C, preferably at 22 to 28 ° C and in particular at 25 ° C and a voltage of 1 to 60 V, preferably 10 to 20 V over a period of 4 min to 24 h, preferably 27 to 33 minutes, and especially 30 minutes, when an oxide layer having a layer thickness in the range of 100 to 1000 nm, for example 200 to 450 nm or 300 to 400 nm and for some purposes preferably 340 to 360 nm generated is to be covered whose entire surface of nanotubes with a diameter in the range of 10 to 300 nm, for example from 20 to 220 nm or even 180 nm, more preferably from 30 to 100 or 40 to 80 nm.

With the method according to the invention, oxide layers which are completely present on the surface in nanostructured form, in particular in the form of nanotubes, on any metals coated with thin oxide layers and / or metal alloys can be produced which completely cover the metals or metal alloys.

The oxide layers on metals or metal alloys according to the invention, which have the above-described nanostructures, in particular nanotubes, ensure excellent adhesion of, for example, adhesives, paints, solder, sealants, bone cement, adhesion promoters or biological tissue as well as other coatings, such as chemical protection coatings or heat. Further, when at least one workpiece has a surface made according to the invention, two such workpieces or one workpiece with one workpiece having a surface of another material can be satisfactorily bonded by merely joining under elevated pressure at room temperature or at elevated temperatures get connected.

However, the surfaces produced according to the invention can also serve for other purposes than the improvement of adhesion. The oxidation and nanostructuring causes changes in the physical and / or chemical interaction of the surface with light or matter. In particular, the reduces electrical conductivity and increases corrosion resistance. Color or emissivity of the surface are also changed.

The large increase in the surface area due to the formation of nanostructures, in particular of nanotubes, can also greatly increase the catalytic effects of the surface itself or of a thin and / or nanoscale coating on the same e.g. with dyes or metal catalysts result because heterogeneous catalysis is known to be a surface phenomenon. Even purely physical phenomena, such as the increase in the number of points at which nuclei or nuclei can form, can be used.

An example of particularly preferred workpieces with surface produced according to the invention are metal prostheses and implants, which are e.g. Titanium or a titanium alloy include. The porous surfaces ensure that the biological materials in the body, with which they are supposed to grow together, stick to them excellently.

The following example explained the invention in more detail.

Examples Comparative Example 1- Anodization of a Ti-6Al-4V surface

• Ein Werkstück aus Ti-6Al-4V mit gebeizter Oberfläche wurde in eine wässrige Elektrolyt-Lösung bei 25°C getaucht, die 130 g/l Ammoniumsulfat und 0,5 g/l Ammoniumfluorid enthielt.

A pickled Ti-6Al-4V surface was anodized as follows:

• A pickled surface Ti-6Al-4V workpiece was immersed in an aqueous electrolyte solution at 25 ° C containing 130 g / L of ammonium sulfate and 0.5 g / L of ammonium fluoride.

Between the Ti-6Al-4V workpiece used as the anode and a noble metal cathode, a voltage of 10 to 25 V was applied for 30 minutes. The resulting surface, which has large areas without structuring (α-phase of the Ti-6Al-4V structure) on the surface in addition to areas with nanotubes, is in Fig. 1 shown.

Comparative Example 2 Nanostructuring of a Ti-6Al-4V surface by means of pulsed laser radiation in an inert atmosphere

A pickled surface Ti-6Al-4V workpiece was scanned once with a diode-pumped Nd: YVO ₄ (neodymium-pumped yttrium orthovanadate) laser (wavelength λ: 1064 nm) under argon atmosphere at ambient pressure and ambient temperature.

• Pp (Impulsspitzenleistung der austretenden Laserstrahlung): 38 kW
• P_m (mittlere Leistung der austretenden Laserstrahlung): 6 W
• t (Impulslänge der Laserimpulse): 17 ns
• f (Repetitionsrate der Laserimpulse) 10 kHz
• v (Abtastgeschwindigkeit an der Werkstückoberfläche): 800 mm/s
• d (Durchmesser des Laserstrahls am Werkstück): 80 µm
• α (Absorption der Laserstrahlung des bestrahlten Material): 15 %
• T_v (Siedepunkt des Materials bei Normaldruck): 3560 K
• c_p (Spezifische Wärmekapazität): 580 J/kgK
• κ (Spezifische Wärmeleitfähigkeit) 22 W/mK

The remaining process parameters were:

• Pp (pulse peak power of the exiting laser radiation): 38 kW
• P _m (mean power of the exiting laser radiation): 6 W
• t (pulse length of the laser pulses): 17 ns
• f (repetition rate of the laser pulses) 10 kHz
• v (scanning speed on the workpiece surface): 800 mm / s
• d (diameter of the laser beam on the workpiece): 80 μm
• α (absorption of the laser radiation of the irradiated material): 15%
• T _v (boiling point of the material at atmospheric pressure): 3560 K
• c _p (specific heat capacity): 580 J / kgK
• κ (specific thermal conductivity) 22 W / mK

This results in ε = 1.2, ie ε is within the range required by Equation 1 above.

The surface obtained is in Fig. 2 shown. It can be seen that the surface has a nodular nanostructure throughout, but no nanotubes.

Example 1. Nanostructuring of a Ti-6Al-4V surface using pulsed laser radiation in an inert atmosphere followed by anodization

A pickled surface Ti-6Al-4V workpiece was scanned once with a diode-pumped Nd: YVO ₄ (neodymium-pumped yttrium orthovanadate) laser (wavelength λ: 1064 nm) under argon atmosphere at ambient pressure and ambient temperature.

The other process parameters were also as described in Comparative Example 2 above.

Subsequently, the workpiece having a nanostructured surface as described above was subjected to anodization as described in Comparative Example 1 above.

The surface obtained is in Fig. 3 shown. It can be seen that the entire surface is covered by fine nanotubes and that there are no unstructured areas.

Comparative Example 3 Nanostructuring of a Ti-6Al-4V surface by means of pulsed laser radiation in a reactive atmosphere

A Ti-6Al-4V pickled surface workpiece was cast once with a diode-pumped Nd: YVO ₄ (neodymium-pumped yttrium orthovanadate) laser (wavelength λ: 1064 nm) under oxygen atmosphere (pressure about 1.5 bar) at ambient temperature sampled.

• Pp (Impulsspitzenleistung der austretenden Laserstrahlung): 38 kW
• P_m (mittlere Leistung der austretenden Laserstrahlung): 6 W
• t (Impulslänge der Laserimpulse): 17 ns
• f (Repetitionsrate der Laserimpulse) 10 kHz
• v (Abtastgeschwindigkeit an der Werkstückoberfläche): 800 mm/s
• d (Durchmesser des Laserstrahls am Werkstück): 80 µm
• α (Absorption der Laserstrahlung des bestrahlten Material): 15 %
• T_v (Siedepunkt des Materials bei Normaldruck): 3560 K
• c_p (Spezifische Wärmekapazität): 580 J/kgK
• κ (Spezifische Wärmeleitfähigkeit) 22 W/mK

The remaining process parameters were:

• Pp (pulse peak power of the exiting laser radiation): 38 kW
• P _m (mean power of the exiting laser radiation): 6 W
• t (pulse length of the laser pulses): 17 ns
• f (repetition rate of the laser pulses) 10 kHz
• v (scanning speed on the workpiece surface): 800 mm / s
• d (diameter of the laser beam on the workpiece): 80 μm
• α (absorption of the laser radiation of the irradiated material): 15%
• T _v (boiling point of the material at atmospheric pressure): 3560 K
• c _p (specific heat capacity): 580 J / kgK
• κ (specific thermal conductivity) 22 W / mK

This results in ε = 1.2, ie ε is in the range according to the invention, which is required by equation 1 above.

The surface obtained is in Fig. 4 shown. It can be seen that the surface despite partial oxidation by the oxygen atmosphere, which was detected by means of photoelectron spectroscopy (XPS analysis), although throughout a nodular nanostructure, but no nanotubes.

Example 2 - Nanostructuring of a Ti-6Al-4V surface by means of pulsed laser radiation in a reactive atmosphere and subsequent anodization

A Ti-6Al-4V pickled surface workpiece was cast once with a diode-pumped Nd: YVO ₄ (neodymium-pumped yttrium orthovanadate) laser (wavelength λ: 1064 nm) under oxygen atmosphere (pressure about 1.5 bar) at ambient temperature sampled.

The other process parameters were also as described in Comparative Example 3 above.

Subsequently, the workpiece having a nanostructured surface as described above was subjected to anodization as described in Comparative Example 1 above.

The surface obtained is in Fig. 5 shown. It can be seen that the entire surface is covered by fine nanotubes and that there are no unstructured areas.

Claims (15)

1. A method for nanostructuring and oxidizing a surface of a material that comprises an anodizable metal and/or an anodizable metal alloy, which can both be at least partially coated with an oxide layer,
   wherein first the surface of the metal and/or of the metal alloy and/or of the oxide layer on the metal and/or the metal alloy, which is accessible to laser irradiation or to irradiation using a particle beam and on which the structures are to be generated, is nanostructured, wherein for generating nanostructures in the form of open-pored, rimose and/or fractal-like nanostructures, in the form of open-pored mountain and valley structures, open-pored undercut structures or cauliflower- or nodule-like structures, the surface is completely scanned once or multiple times using a pulsed laser beam, or a continuous particle beam, which is selected from an electron beam or an ion beam or an uncharged particle beam or a combination thereof, in such a way that neighboring light spots of the laser beam or scanning spots of the particle beam abut each other without gaps or overlap each other, wherein the following conditions are adhered to:

   when scanning is carried out using a laser beam and the pulse duration of the laser pulses t is 0.1 ns to 2000 ns, $$\mathrm{an}\mathit{\epsilon }-\mathrm{value\; of}\mathrm{0.07}\le \mathit{\epsilon }\le \mathrm{2300},$$

   

   wherein $$\epsilon =\frac{P_P^2\cdot \sqrt{P_m}\cdot f\cdot \alpha \cdot \sqrt{t}\cdot \sqrt{\kappa }}{d^2\cdot \sqrt{v}\cdot \sqrt{T_V}\cdot \sqrt{c_P}\cdot \sqrt{\lambda }}\cdot {10}^3$$

   

   or,
   when scanning is carried out using a laser beam at a wavelength of the laser λ of 100 ≤ λ ≤ 11,000 nm, and the pulse duration of the laser pulses t < 0.1 ns, $${\mathrm{an}\mathrm{\epsilon }}_1-\mathrm{value\; of}\mathrm{0.5}\le {\mathrm{\epsilon }}_1\le 1650,$$

   

   wherein $${\epsilon }_1=\frac{P_P\cdot \sqrt{P_m}\cdot f\cdot \alpha \cdot \sqrt{t}\cdot \sqrt{\kappa }}{d^2\cdot \sqrt{v}\cdot \sqrt{T_V}\cdot \sqrt{c_P}}\cdot {10}^3$$

   

   wherein in Equation 1 and Equation 2:

   P_p: pulse peak power of the exiting radiation [kW];

   t: pulse duration of the pulses [ns];

   f: repetition rate of the radiation pulses [kHz];

   v: scanning speed on the workpiece surface [mm/s];

   d: diameter of the energetic radiation on the material surface [µm];

   α: absorption of the energetic radiation of the irradiated material [%] at the incident wavelength under normal conditions;

   or,

   when scanning is carried out using a particle beam, $${\mathrm{an}\mathit{\epsilon }}_{\mathrm{2}}-\mathrm{value\; of}\mathrm{0.5}\le {\mathit{\epsilon }}_{\mathrm{2}}\le \mathrm{1550},$$

   

   wherein $${\epsilon }_2=\frac{P_m^2\cdot \sqrt{\kappa }\cdot \alpha }{\sqrt{d^3}\cdot \sqrt{v}\cdot \sqrt{T_V}\cdot \sqrt{c_P}}\cdot {10}^2$$

   

   wherein in Equation 3:

   v: scanning speed on the workpiece surface [mm/s];

   d: diameter of the energetic radiation on the material surface [µm]; with the proviso that d/v < 7000 ns;

   α: absorption of the energetic radiation of the radiated material [%] under normal conditions;

   and wherein in Equation 1, Equation 2 and Equation 3:

   P_m: average power of the exiting radiation [W];

   T_v: evaporation or decomposition temperature of the material [K] at normal pressure;

   c_p: specific heat capacity [J/kgK] at normal conditions;

   K: specific thermal conductivity [W/mK] at normal conditions and averaged across the different spatial directions;

   wherein the atmosphere in which the method is carried out is
   a vacuum or a gas or gas mixture that is inert with respect to the surface under the method conditions, or
   a gas or gas mixture that is reactive with respect to the metal and/or the metal alloy and/or the oxide layer on the metal and/or the metal alloy of the surface under the method conditions, the gas or gas mixture chemically modifying the metal and/or the metal alloy and/or the oxide layer on the metal and/or the metal alloy during or after scanning using the laser beam or particle beam compared to the composition of the same prior to scanning using the laser beam or particle beam;
   and the surface having nanostructures is subsequently anodized by immersion in an electrolyte solution, which contains both an oxidizing agent and an agent dissolving the oxide again, which may optionally be identical to the oxidizing agent, by connecting to a cathode, and by applying a voltage.
2. The method according to claim 1, wherein the metal or the metal alloy is selected from aluminum, titanium, magnesium, iron, cobalt, zinc, niobium, zirconium, hafnium, tantalum, vanadium and/or the alloys thereof, and steel.
3. The method according to claim 1 or 2, wherein, when the atmosphere is a vacuum, the pressure is in the range of 10^-17 bar to approximately 10^-4 bar, when the atmosphere is a gas or a gas mixture that is inert or reactive with respect to the surface under the conditions of the method the pressure is in the range of approximately 10^-6 bar to approximately 1 bar when using particle radiation, and up to 15 bar when using laser radiation, and the temperature outside the laser beam or particle beam is in the range of approximately -50°C to approximately 350°C.
4. A method according to any one of claims 1 to 3, wherein approximately 0,07 ≤ ε ≤ approximately 2000, more preferably approximately 0.07 ≤ ε ≤ approximately 1500.
5. A method according to any one of claims 1 to 4, wherein in Equation 1 the pulse duration of the laser pulses t is approximately 0.1 ns to approximately 300 ns, more preferably approximately 5 ns to approximately 200 ns and/or the pulse peak power of the exiting laser radiation P_p is approximately 1 kW to approximately 1800 kW and/or the average power of the exiting laser beam P_m is approximately 5 W to approximately 28,000 W and/or the repetition rate of the laser pulses f is approximately 10 kHz to approximately 3000 kHz and/or the scanning speed on the workpiece surface v is approximately 30 mm/s to approximately 19,000 mm/s and/or the diameter of the laser beam on the workpiece d is approximately 20 µm to approximately 4500 µm.
6. A method according to any one of claims 1 to 3, wherein approximately 0.7 ≤ ε₁ ≤ approximately 1500, more preferably approximately 0.9 ≤ ε₁ ≤ approximately 1200.
7. A method according to any one of claims 1 to 3 and 6, wherein in Equation 2 the pulse duration of the radiation t is approximately 0.005 ns to approximately 0.01 ns, preferably approximately 0.008 ns to approximately 0.01 ns and/or the pulse peak power of the exiting radiation P_p is approximately 100 kW to approximately 30,000 kW, preferably approximately 150 kW to approximately 25,000 kW and/or the repetition rate of the radiation f is preferably approximately 100 kHz to approximately 80,000 kHz, more preferably approximately 120 kHz to approximately 20,000 kHz and/or the average power of the exiting particle radiation P_m is approximately 1 W to approximately 25,000 W, preferably approximately 20 W to approximately 9500 W and/or the scanning speed on the workpiece surface v is approximately 30 mm/s to approximately 60,000 mm/s, preferably approximately 200 mm/s to approximately 50,000 mm/s and/or the diameter of the laser beam on the workpiece d is approximately 20 µm to approximately 4500 µm, preferably approximately 50 µm to approximately 3500 µm.
8. A method according to any one of claims 1 to 3, wherein approximately 0.7 ≤ ε₂ ≤ approximately 1400, more preferably approximately 0.9 ≤ ε₂ ≤ approximately 1100.
9. A method according to any one of claims 1 to 3 and 8, wherein in Equation 3 the average power of the exiting radiation P_m is approximately 1 W to approximately 25,000 W, preferably approximately 20 W to approximately 9500 W and/or the scanning speed on the workpiece surface v is approximately 100 mm/s to approximately 8,000,000 mm/s, preferably approximately 200 mm/s to approximately 7,000,000 mm/s and/or the diameter of the particle beam on the workpiece d is approximately 20 µm to approximately 4500 µm, preferably approximately 50 µm to approximately 3500 µm, with the proviso that the ratio of the diameter of the particle beam on the workpiece to the scanning speed d/v < approximately 7000 ns.
10. A method according to any one of claims 1 to 9, wherein the metal and/or the metal alloy is titanium and/or a titanium alloy.
11. A method according to any one of claims 1 to 10, wherein the electrolyte solution contains fluoride ions.
12. The method according to claim 11, wherein the electrolyte solution contains 10 to 1000 g/l ammonium sulfate and 0.1 to 10 g/l ammonium fluoride and is free of hydrofluoric acid.
13. The method according to claim 12, wherein the voltage is 10 to 60 volts, and the anodizing is carried out at a temperature of 20 to 50 °C over a time period of 4 minutes to 24 hours.
14. A method according to any one of claims 1 to 13, wherein the metal or the metal alloy is completely covered by metal oxide or metal alloy oxide, which on the entire surface thereof has surface structures in the nanometer range, and in the case of titanium or a titanium alloy in particular has nanotubes preferably having a diameter of 10 to 300 nm.
15. A method according to any one of claims 1 to 14, wherein the surface obtained by the method is joined to a further material, which is selected in particular from inorganic materials, organic materials, inorganic-organic materials, such as complex compounds, composite materials made of inorganic materials and organic materials, and biological materials.

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